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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>计算梯形稻田面积</title>
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<body>
    <script>
        document.write("<pre>")
            var a = 30;
            var b = 50;
            var c = 30;
            var d= (a+b)*c/2
            document.write("梯形稻田的面积为："+d);
        document.write("</pre>")
    </script>
</body>
</html>